Prior to the great overseas voyages in the 16th and 17th century, woad was the European version of indigo and was the primary blue dye for textiles.
Woad is also a plant, which can be used to extract indigo blue pigment. This plant has oblong leaves and small yellow bunches of flowers, and grows approximately 90cm high.
Woad favours mild climates, growing in regions such as the Netherlands, Germany (Thüringen), France (Toulouse, Languedoc) and England (Northumbria). In the Middle Ages, woad was considered the queen of medieval dyes, partly due to its high value to the economy. See also ‘Indigo’.
Source: Nouvelle de Nîmes Nº 5: The Denim Dictionary